/Engine/Source/Runtime/CoreUObject/Public/UObject/Class.h
Initializes the ClassReps and NetFields arrays used by replication. This happens lazily based on the CLASS_ReplicationDataIsSetUp flag, and will generally occur in Link or PostLoad. It's possible that replicated UFunctions will load after their owning class, soUFunction::PostLoadwill clear the flag on its owning class to force lazy initialization next time the data is needed. Also happens after blueprint compiliation.
void SetUpRuntimeReplicationData()